I. Field of the Invention
This invention is concerned with a ribbon or tape for use in non-impact printing, and more particularly, to a method for the preparation of a fluorescent ink coating that is applied to a ribbon to make a fluorescent thermal transfer ribbon. The method by which the fluorescent ink coating is made is a monomer polymerization method.
II. Description of the Prior Art
It is known in prior art to use ribbons in thermal transfer imaging processes. In these processes, thermal means are used to selectively heat areas of ribbon having an image transfer layer or coating. The printing is generally achieved by heat transferring the coating from the ribbon to paper by the local heating of the ribbon. Such image-localized heating may be accomplished by contacting the ribbon with point electrodes or some sort of heating element and a broad area contact electrode or heating element. The high current densities in the area of the electrodes during the application of the applied voltage produces intense local heating which causes transfer of the coating from the ribbon to either paper or any receiving medium adjacent to or in contact with the ribbon. Various publications such as IBM Technical Disclosure Bulletin entitled "Resistive Ribbon Thermal Transfer Printing Method", Crooks, et al., vol. 19, No. 11, April, 1977, p. 4396 illustrate this general thermal transfer technique. Printers and various other hardware used in these methods are disclosed in, for example, U.S. Pat. Nos. 4,326,812; 4,327,365 and 4,329,071.
The ink and substrate are basically the keys to a thermal transfer technique. Various known prior art substrates have been used including Mylar, condenser paper, other polyesters and conductive polyurethanes. Of these, two substrates are most commonly used, i.e., Mylar and special condenser paper. Mylar is a registered trademark of DuPont. The preferred Mylar ranges in thickness from about 3.5 to 6 microns and the special condenser paper ranges in thickness from about 10 to 13 microns. Condenser paper is used in thermal line printers in widths ranging from about 33 to 267 mm. (The low tear strength of the condenser paper precludes its use for narrower ribbons.) Polyester film like Mylar is found in thermal serial printers in common widths of about 6.35, 8.0 and 12.7 mm. The length of both condenser paper and polyester film depends upon the space available in the printer or ribbon cassettes. There are other substrates known to be adapted for use in thermal transfer ribbons such as those are described in U.S. Pat. Nos. 4,103,066, 4,269,892, 4,291,994 and 4,320,170.
In the machine processing of various types of information contained on tickets, tags, labels, postage imprints and the like, it is generally known to employ detectors which are responsive to shape relationships and/or colors, and in many cases to the fluorescence of an ink which may be excited, for example, by ultraviolet light. Fluorescent inks and dyes have long been known such as, for example, those disclosed in U.S. Pat. Nos. 2,681,317, 2,763,785, 3,230,221, 3,412,104, 3,452,075, and 3,560,238. The fluorescent inks and the methods of making or using them as known in the prior art, generally entail the use of a fluorescent ink which, when irradiated, will fluoresce and emit radiation within the wavelength for the particular fluorescent color of that dye or ink. It is known, for example, in the postage meter art to provide a red fluorescent ink for machine reading of processed mail.
It is therefore desirable to provide a thermal transfer ribbon having a fluorescent ink layer thereon so that items such as tickets, tags, labels, postage imprints and the like can be imprinted with indicia such as alphanumerics, bar code, slogans etc., by the use of such fluorescent thermal transfer ribbon. However, known prior art methods used for the preparation of fluorescent inks generally use a technique that employs a dispersion of resins and dyes. This type of technique has the following disadvantages: (1) It produces an ink with an inhomogeneous dye distribution. (2) It produces an ink having a large dye particle size (3-30 m) and a broad particle size distribution. (3) It also produces an ink that prints a fluorescent image having a weak intensity of fluorescence and, in general, a short life time of fluorescence.
In U.S. Pat. No. 4,172,064, there is disclosed an aqueous copolymer coating system adapted for forming abrasion-resistant coatings using either printing or coating processes. The copolymer employed in the coating system includes: (a) a four component (monomer) copolymer comprising: (1) an alkyl methacrylate, (2) an alkyl acrylate, (3) unsaturated nitrile, and (4) unsaturated organic acid; (b) at least one coalescing agent for the ether-alcohol types; (c) at least one surfactant agent which may be either of the substituted polyether non-ionic type or one of a group of selected anionic agents; and (d) one or more additives as may be necessary to impart color, control foam, and prevent mildew and/or fungus attack. Basically, this patent is concerned with printing ink copolymers and has no disclosure or suggestion of the idea of a fluorescent coating or printing an indicia which is fluorescent. Furthermore, unlike the present invention, the process described by this patent (i) does not involve a chemical reaction between the dyes and monomers, i.e., a chemical bonding between dye and basic monomer resulting in stronger intensity and longer lifetime of fluorescence, (ii) does not treat a fluorescent dye with an acid monomer to put the dye in acidic form followed by treatment with a basic monomer and (iii) does not describe a fluorescent dye which is incorporated in the monomers (describes a dye dispersed in an emulsion medium).